The advent of wide-bandgap (WBG) devices like silicon carbide (SiC) MOSFETs has resulted in a paradigm shift toward high-density and high-efficiency integration of power electronics systems. This being the result of relatively high switching frequencies (>10 kHz) compared to conventional Si IGBT counterparts, which reportedly can minimize the size of passive components such as DC-link capacitors and line harmonic filters. Unfortunately, with faster switching speeds and high slew rates, the common-mode (CM) and differential-mode (DM) conducted emissions interference (EMI) noise is worsened. The effects are manifested at the utility interface with grid-tied applications (three-phase rectifiers or back-to-back converters) in the form of high CM and DM emissions, total harmonic distortion (THD) and current harmonics. While at the motor end, long cable and bearing/leakage current effects are prevalent. As such, typically bulky passive filters are recommended to comply with industry regulations and allow safe and reliable system operation, which can be detrimental on the overall system power density. Hence, it is imperative to minimize the filter volume/weight contribution to fully utilize the benefits of WBG power converters. As an added feature, modular filter building block (FBB) configurations inspired by the building block nature of power electronics converters are needed to address scalability to higher power levels (through interleaving or paralleling) without the need for significant filter redesign. As such, for grid-tied applications (AC-DC converters), the interleaving of parallel converters adopted to achieve superior harmonic attenuation for grid-side currents at the expense of low harmonic filter volume. Therefore, interleaved converters are explored in Chapters 2 and 3. However, to block inter-channel circulation, additional use of coupled inductors (CI) can outweigh the benefits of interleaving. Therefore, modular FBB architectures with unique methods to handle circulating currents are proposed. At the same time, the FBB is designed to meet power quality and EMI limits for any given number of channels, up to the maximum number of channels, N, allowed at the point of common coupling (PCC). Consequently, a qualitative and quantitative comparison of FBB candidates is performed, and the indirectly coupled FBB using a secondary loop interconnection is proposed as a viable modular FBB candidate. Correspondingly, for DC-AC inverters, modular filters can be realized using a masked impedance and decoupling approach. The test case being a DC-fed motor drive for aircraft propulsion systems. Techniques, such as optimized parallel RC dampers to reduce the peak bearing current and CM/DM magnetic integration of a DC side filter with an embedded DC current sensor and embedded decoupling path with gate driver for high frequency commutation, are implemented to reduce the overall weight of the system. The challenges with low temperature rise margin due to high ambient temperature and low peak Partial Discharge Inception Voltage (PDIV) are addressed. In addition, a novel pulse with modulation (PWM) scheme is proposed to further enhance the bandwidth of the proposed AC filter, specifically targeted to reduce the peak bearing current and improve the specific power and motor lifetime. A negative consequence of high-density filter integration is the impact of self and mutual parasitic couplings of filter sub-components on filter attenuation, which is studied on a back-to-back converter system (AC-AC). Simplified lumped models that are representative of the high frequency filter behavior are developed to desensitize the impact of individual filter sub-components. Thereafter, unique winding and placement techniques are proposed to compensate for the impact of self and mutual parasitic couplings on the noise spectrum. Overall, this work presents potential FBB topologies for varying modes of power conversion (AC-DC, DC-AC, and AC-AC), ultimately aimed at reducing the volume/weight of the system. Methods to minimize the passive component volume/weight from the point of view of topology, magnetic integration, and PWM techniques are discussed, while the implications of a high-density integration at high frequency is presented. Generalized practical design guidelines are formulated to aid in accurate high-density filter design for WBG converters. / Doctor of Philosophy / With the ever-increasing use of switching converters, either AC-DC, DC-AC, or DC-DC converters, electromagnetic interference issues can affect the overall system performance, which necessitates the use of filters. This is especially true with more and more point-of-load applications (parallel converters in charging stations, industries, and residential loads), distributed energy sources (solar power, wind power, and battery storage systems), and primary sources (power plants) being integrated together into a super grid. Similarly, transportation applications (electric vehicles, more-electric aircrafts) demand strict filtering requirements, due to the prime importance of reliability. Therefore, three-phase power quality and EMI filters are an integral part of any power conversion system, from low to high power applications. First, novel techniques to address the scalability and modularity of filters with parallel converters are considered (grid-tied application), where the benefits of interleaving and challenges in circulating current mitigation are addressed. The idea is simply to design one filter that can be used with any given number of converters running in parallel, which promotes rapid manufacturability to meet the ever-increasing demand. Thereafter a highly integrated and optimized filter structure is demonstrated for a traction inverter used in aerospace propulsion. Challenges pertaining to compact filter design are addressed, and new methods are proposed to overcome some of the critical issues that come with high-altitude operation, such as reliability, high temperature, and partial discharge-free operation. Lastly, the effect of non-idealities on filters that can lead to deteriorated performance is explored. As such, solutions to compensate for these effects are proposed and verified. Clearly, there is a need to optimize filters as well, minimizing their volume and weight contribution within a power converter. This aspect is considered throughout the work where design guidelines are proposed to optimize the given filter topology, filter parameter selection, and form factors for different applications, ranging from AC-DC converters to DC-AC traction motor drives.

The still increasing demand of electrical energy and the rising popularity of renewable energy sources in today's world are two important developments that necessitate the need for innovative solutions in the field of power electronics. Parallel operation of converters is one possible method in trying to bridge an increased current demand. The classical two-level converters, which are the standard in low voltage applications, are rarely adopted in medium and high voltage applications due to the voltage limits on power semiconductor devices. That is one reason for the growing popularity of multilevel converter topologies in medium and high-voltage applications. Although an increase in the number of voltage levels of a multilevel converter has its advantages, there are also challenges posed due to the increased number of switching devices. This has resulted in three-level converters being the most popular compared to converters of higher voltage levels. In this dissertation, the unified operation of parallel connected three-level converter units as a multilevel converter of higher voltage levels is proposed. The mathematical basis for operating parallel connected converter units as a single multilevel converter and the governing equations for such systems are derived. The analysis and the understanding of these equations are important for assessing practicality of the system and devising appropriate control structures. Parallel operation of converter units operating as multilevel converter have their own set of challenges, the two foremost being that of load-sharing and the possibility of circulating and cross currents. Developing solutions to address these challenges require a thorough understanding of how these manifest in the proposed system. Algorithms are then developed for tackling these issues. The control structures are designed and the developed algorithms are implemented. The operation of the system is verified experimentally. / Die weiterhin steigende Nachfrage nach elektrischer Energie und die zunehmende Verwendung erneuerbarer Energiequellen in der heutigen Welt sind zwei wichtige Entwicklungen, die die Notwendigkeit innovativer Lösungen im Bereich der Leistungselektronik erfordern. Der Parallelbetrieb von Stromrichtern ist eine mögliche Methode, um einen erhöhten Strombedarf zu decken. Der klassische Zweipunkt-Spanungszwischenkreisstromrichter, der bei Niederspannungsanwendungen weit verbreitet ist, wird aufgrund der Spannungsgrenzen für Leistungshalbleiterbauelemente zunehmend weniger in Mittel- und Hochspannungsanwendungen eingesetzt. Die begrenzte Spannungsbelastbarkeit der Leistungshalbleiterbauelemente ist ein Grund für die wachsende Beliebtheit von Mehrpunkt-Stromrichtertopologien in Mittelund Hochspannungsanwendungen. Obwohl eine Erhöhung der Anzahl der Spannungsstufen eines Mehrpunkt-Stromrichters Vorteile hat, gibt es auch Herausforderungen und Nachteile aufgrund der erhöhten Anzahl von Leistungshalbleitern. Dies hat dazu geführt, dass der Dreipunkt-Stromrichter die verbreiteste Topologie im Vergleich zu anderen Stromrichtern mit einer höheren Anzahl von Spannungsstufen ist. In dieser Dissertation wird der Betrieb von parallel geschalteten Dreipunkt-Stromrichtereinheiten als ein Mehrpunkt-Stromrichter mit erhöhter Anzahl an Spannungsstufen vorgeschlagen. Die mathematische Basis für den Betrieb von parallel geschalteten Stromrichtereinheiten als ein Mehrpunkt-Stromrichter und die beschreibenden Gleichungen eines solchen Systems werden abgeleitet. Die Analyse und das Verständnis dieser Gleichungen sind wichtig für die Beurteilung der Praktikabilität des Systems und die Erarbeitung geeigneter Regelstrukturen. Der parallele Betrieb von Stromrichtereinheiten hat seine eigenen Herausforderungen, wobei die beiden wichtigsten die Lastverteilung und die Möglichkeit von Kreis- und Querströmen sind. Die Entwicklung von Lösungen zur Bewältigung dieser Herausforderungen erfordert ein gründliches Verständnis dafür, wie sich diese Phänomene in dem vorgeschlagenen System manifestieren. Algorithmen zur Lösung dieser Probleme werden anschlieend entwickelt. Die Regelstrukturen werden entworfen und die entworfenen Algorithmen implementiert. Die Funktionsweise des Systems wird experimentell überprüft.

[ES] En este trabajo se proponen técnicas de control específicas para la paralelización de inversores sin transformador conectados a red, en aplicaciones de interconexión de buses de microrredes híbridas e instalaciones fotovoltaicas de gran potencia. La paralelización de inversores presenta múltiples ventajas como la modularidad, la redundancia o la flexibilidad para ampliar la potencia de un sistema o de una instalación. En el caso de inversores fotovoltaicos centralizados, también permite la conexión/desconexión de módulos inversores conectados en paralelo permitiendo una mayor eficiencia global cuando se trabaja a bajas potencias. Sin embargo, la paralelización de inversores provoca la aparición de corrientes de circulación que pueden provocar efectos indeseables en el sistema o en la instalación. Las contribuciones que se llevan a cabo en esta tesis están todas ellas orientadas a la mejora de la operación de inversores en paralelo en las aplicaciones descritas y son las siguientes: 1) Se presenta un modelo preciso en pequeña señal de n inversores conectados en paralelo con filtro de conexión a red LCL, en el cual se tienen en consideración los términos de acoplamiento entre fases de los inductores trifásicos. 2) Se propone una técnica de control en la que se emplean n-1 lazos de regulación que controlan la componente homopolar de las corrientes e imponen un valor nulo en régimen permanente, a fin de eliminar las corrientes de circulación. 3) Se propone el uso de moduladores en espacio vectorial de tres dimensiones (3D-SVM) para implementar el control de la componente homopolar de las corrientes. 4) Se muestran resultados analíticos, de simulación y experimentales que validan el esquema de control propuesto considerando la aparición de corrientes de circulación debido a distintos factores: desbalanceo de inductancias entre las fases de un inversor y de distintos inversores, desbalanceo de potencia entre inversores y empleo de modulaciones distintas en los inversores conectados en paralelo. Los ensayos experimentales se realizan sobre un convertidor trifásico de 10 kW formado por la conexión en paralelo de dos módulos de 5 kW cada uno. 5) Se muestran resultados de simulación y experimentales de la aplicación de las técnicas de reducción de corrientes de circulación a convertidores de interconexión entre los buses de alterna y continua de microrredes híbridas. Los ensayos experimentales se particularizan a un convertidor trifásico de 7.5 kW formado por un módulo de 5 kW y otro de 2.5 kW conectados en paralelo, emulando una eventual ampliación de potencia del 50%. 6) Se lleva a cabo el estudio por simulación de un sistema fotovoltaico de 2 MW compuesto por cuatro inversores de 500 kW conectados en paralelo, demostrando que el control de las componentes homopolares de las corrientes reduce en gran medida el valor de las corrientes de circulación y mejora el desempeño de la instalación. 7) Por último, se propone una técnica de control para mejorar la eficiencia global de inversores fotovoltaicos centralizados de potencia elevada, el cual se basa en la utilización de modelos funcionales bidimensionales de eficiencia para activar/desactivar los módulos de potencia en función del punto de operación del campo fotovoltaico. / [CA] En aquest treball es proposen tècniques de control específiques per a la paral·lelització d'inversors sense transformador connectats a la xarxa, en aplicacions d'interconnexió de busos de micro-xarxes híbrides i instal·lacions fotovoltaiques de gran potència. La paral·lelització d'inversors presenta múltiples avantatges com ara són la modularitat, la redundància o la flexibilitat per ampliar la potència d'un sistema o d'una instal·lació. En el cas d'inversors fotovoltaics centralitzats, també es permet la connexió/desconnexió de mòduls inversors connectats en paral·lel permetent una major eficiència global quan es treballa a potències baixes. En canvi, la paral·lelització d'inversors provoca l'aparició de corrents de circulació que poden provocar efectes indesitjables en el sistema o en la instal·lació. Totes les contribucions que es porten a terme en aquesta tesi estan orientades a la millora de la operació de inversors en paral·lel en les aplicacions descrites i son les següents: 1)Es presenta un model precís en xicoteta senyal de n inversors connectats en paral·lel amb filtre LCL de connexió a xarxa, en el qual es tenen en consideració els termes d'acoblament entre fases dels inductors trifàsics. 2) Es proposa una tècnica de control en la que s'usen n-1 llaços de regulació que controlen la component homopolar de les corrents i imposen un valor nul en règim permanent, a la fi d'eliminar les corrents de circulació. 3) Es proposa l'ús de moduladors en espai vectorial de tres dimensions (3D SVM) per implementar el control de la component homopolar de les corrents. 4) Es mostren resultats analítics, de simulació i experimentals els quals validen l'esquema de control proposat considerant l'aparició de corrents de circulació degut a diversos factors: desbalanceig d'inductàncies entre les fases d'un inversor i de distints inversors, desbalanceig de potència entre inversors i ús de modulacions distintes en els inversors connectats en paral·lel. Els assajos experimentals es realitzen sobre un inversor trifàsic de 10 kW format per la connexió en paral·lel de dos mòduls de 5 kW cadascun. 5) Es mostren resultats de simulació i experimentals de l'aplicació de les tècniques de reducció de corrents de circulació a convertidors d'interconnexió entre els busos d'alterna i contínua de micro-xarxes híbrides. Els assajos experimentals es particularitzen a un convertidor trifàsic de 7.5 kW format per un mòdul de 5 kW i altre de 2.5 kW connectats en paral·lel, emulant una eventual ampliació de potència del 50 %. 6) Es duu a terme l'estudi per simulació d'un sistema fotovoltaic de 2 MW format per quatre inversors de 500 kW connectats en paral·lel demostrant que el control de les components homopolars de les corrents redueixen en gran mesura el valor de les corrents de circulació i millora l'acompliment de la instal·lació. 7) Per últim, es proposa una tècnica de control per a la millora de l'eficiència global d'inversors fotovoltaics centralitzats de potència elevada, el qual es basa en la utilització de models funcionals bidimensionals d'eficiència per activar/desactivar els mòduls de potència en funció del punt d'operació del camp fotovoltaic. / [EN] In this work they have been proposed specific control techniques for the parallelization of transformerless inverters connected to the grid in two specific applications: i) the interlinking converter between ac and dc bus of hybrid microgrids and ii) high power photovoltaic farms. Paralleling of inverters presents some advantages as modularity, redundancy or flexibility for increasing the power of a system or of a plant. In photovoltaic centralized inverters, the parallel inverters can be connected and disconnected in order to improve the global efficiency when the system works at low power. However, the inverters paralleling causes the appearance of circulating currents which can produce undesirable effects in the system or in the plant. The contributions that are carried out in this thesis are all of them aimed at improving the operation of parallel inverters in the described applications and they are as follows: 1) It has been presented an accurate small signal model of n parallel inverters with an LCL grid filter, in which the mutual coupling terms of the three-phase inductors has been considered. 2) It has been proposed a control technique with n-1 control loops that control the zero-sequence current component by setting a zero value in steady state, looking for eliminating the circulating currents. 3) It has been proposed the use of three-dimension space vector modulator (3D SVM) to implement the zero-sequence currents control. 4) The analytical results have been validated by means of simulation and experimental results, showing the performance of the proposed control scheme considering the appearance of circulating currents due to different factors: i) inductor imbalances between the phases of an inverter or ii) between different inverters, iii) power imbalances between inverters and iv) the use of different modulation techniques in the parallel inverters. The experimental tests have been carried out on a 10 kW three-phase converter composed by the parallel connection of two 5 kW modules. 5) They have been shown both simulation and experimental results of the application of circulating current reduction techniques to interlinking converters between the DC and the AC buses of hybrid microgrids. The experimental tests have been particularized to a 7.5 kW three-phase converter composed by a 5 kW and a 2.5 kW module connected in parallel, emulating an eventual 50 % power expansion. 6) Is has been carried out the simulation study of a 2 MW photovoltaic system composed by four 500 kW inverters connected in parallel, showing that the control of the zero-sequence currents greatly reduces the value of the circulating currents and improve the system performance. 7) Finally, it has been proposed a control technique for the improvement of the global efficiency of high power photovoltaic centralized inverters, which is based in the use of bidimensional functional efficiency models to activate/deactivate the power modules according to the operation point of the photovoltaic farm. / Liberos Mascarell, MA. (2021). Técnicas de control para la conexión en paralelo de inversores aplicadas a convertidores de interconexión entre los buses de CC y CA de microrredes híbridas e inversores fotovoltaicos centralizados de alta potencia [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/168190 / TESIS

The still increasing demand of electrical energy and the rising popularity of renewable energy sources in today's world are two important developments that necessitate the need for innovative solutions in the field of power electronics. Parallel operation of converters is one possible method in trying to bridge an increased current demand. The classical two-level converters, which are the standard in low voltage applications, are rarely adopted in medium and high voltage applications due to the voltage limits on power semiconductor devices. That is one reason for the growing popularity of multilevel converter topologies in medium and high-voltage applications. Although an increase in the number of voltage levels of a multilevel converter has its advantages, there are also challenges posed due to the increased number of switching devices. This has resulted in three-level converters being the most popular compared to converters of higher voltage levels. In this dissertation, the unified operation of parallel connected three-level converter units as a multilevel converter of higher voltage levels is proposed. The mathematical basis for operating parallel connected converter units as a single multilevel converter and the governing equations for such systems are derived. The analysis and the understanding of these equations are important for assessing practicality of the system and devising appropriate control structures. Parallel operation of converter units operating as multilevel converter have their own set of challenges, the two foremost being that of load-sharing and the possibility of circulating and cross currents. Developing solutions to address these challenges require a thorough understanding of how these manifest in the proposed system. Algorithms are then developed for tackling these issues. The control structures are designed and the developed algorithms are implemented. The operation of the system is verified experimentally. / Die weiterhin steigende Nachfrage nach elektrischer Energie und die zunehmende Verwendung erneuerbarer Energiequellen in der heutigen Welt sind zwei wichtige Entwicklungen, die die Notwendigkeit innovativer Lösungen im Bereich der Leistungselektronik erfordern. Der Parallelbetrieb von Stromrichtern ist eine mögliche Methode, um einen erhöhten Strombedarf zu decken. Der klassische Zweipunkt-Spanungszwischenkreisstromrichter, der bei Niederspannungsanwendungen weit verbreitet ist, wird aufgrund der Spannungsgrenzen für Leistungshalbleiterbauelemente zunehmend weniger in Mittel- und Hochspannungsanwendungen eingesetzt. Die begrenzte Spannungsbelastbarkeit der Leistungshalbleiterbauelemente ist ein Grund für die wachsende Beliebtheit von Mehrpunkt-Stromrichtertopologien in Mittelund Hochspannungsanwendungen. Obwohl eine Erhöhung der Anzahl der Spannungsstufen eines Mehrpunkt-Stromrichters Vorteile hat, gibt es auch Herausforderungen und Nachteile aufgrund der erhöhten Anzahl von Leistungshalbleitern. Dies hat dazu geführt, dass der Dreipunkt-Stromrichter die verbreiteste Topologie im Vergleich zu anderen Stromrichtern mit einer höheren Anzahl von Spannungsstufen ist. In dieser Dissertation wird der Betrieb von parallel geschalteten Dreipunkt-Stromrichtereinheiten als ein Mehrpunkt-Stromrichter mit erhöhter Anzahl an Spannungsstufen vorgeschlagen. Die mathematische Basis für den Betrieb von parallel geschalteten Stromrichtereinheiten als ein Mehrpunkt-Stromrichter und die beschreibenden Gleichungen eines solchen Systems werden abgeleitet. Die Analyse und das Verständnis dieser Gleichungen sind wichtig für die Beurteilung der Praktikabilität des Systems und die Erarbeitung geeigneter Regelstrukturen. Der parallele Betrieb von Stromrichtereinheiten hat seine eigenen Herausforderungen, wobei die beiden wichtigsten die Lastverteilung und die Möglichkeit von Kreis- und Querströmen sind. Die Entwicklung von Lösungen zur Bewältigung dieser Herausforderungen erfordert ein gründliches Verständnis dafür, wie sich diese Phänomene in dem vorgeschlagenen System manifestieren. Algorithmen zur Lösung dieser Probleme werden anschlieend entwickelt. Die Regelstrukturen werden entworfen und die entworfenen Algorithmen implementiert. Die Funktionsweise des Systems wird experimentell überprüft.

Only in English.

There is currently a high demand for electric power from renewablesources. One source that remains relatively untapped is the motionof ocean waves. Anders Hagnestål has been developing a uniquelyefficient and simplified design for a point-absorb buoy generator byconverting its linear motion directly into alternating electric power usinga linear PM engine. To test this method, a smaller prototype isbuilt. Its characteristics present some unusual challenges in the designand construction of its winding.Devices of this type typically use relatively low voltage (690V typicallyfor a wind turbine, compared to the 10kV range of traditionalpower plants). To achieve high power, they need high current, whichin turn requires splitting the conductors in the winding into isolatedparallel strands to avoid losses due to eddy currents and current crowding.However, new losses from circulating currents can then arise. Inorder to reduce said losses, the parallel conductors should be transposedin such a way that the aggregate electromotive force the circuitsthat each pair of them forms is minimized.This research and prototyping was performed in absence of advancedindustrial means of construction, with limited space, budget,materials, manpower, know-how, and technology. Manual ingenuityand empirical experimentation were required to find a practical implementationfor: laying the cables, fixing them in place, transferringthem to the machine, stripping their coating at the ends and establishinga reliable connection to the current source.Using theoretical derivations and FEM simulation, a sufficientlygood transposition scheme is proposed for the specific machine thatthe winding is built for. A bobbin replicating the shape of the enginecore is built to lay down the strands.The parallel strands are then organized each into their respectivebobbin, with a bobbin rack and conductor funneling device being designedand constructed to gather them together into a strictly-organizedbundle. An adhesive is found to set the cables in place.Problems with maintaining the orientation and configuration of thecables in the face of repeated torsion are met and solved. A chemicalsolution is used to strip the ends of the conductors, and a reliableconnection is established by crimping the conductors into a bi-metalCu-Al lug.ivIn conclusion, the ideal transposition schemes required to cancelout circulating currents due to magnetic flux leakage are impossibleto put in practice without appropriate technological means. The feasibletransposition scheme turns out to be a simple mirroring of conductors’positions, implemented by building each half of the windingseparately around replicas of the core and then connecting them usingcrimping lugs. / Efterfrågan på el från förnybara källor är hög och inget tyder på att det kommer ändras den närmsta tiden. En källa till förnybar el som än idag står relativt orörd är den där man använder energin från havsvå- gor. Det är denna förnybara källa Anders Hagnestål haft i åtanke när han nu bygger en unikt effektiv generator med syftet att i ett senare skede utvinna el med hjälp av flytande punktabsorberande vågkraft- system. Generatorn är av den linjära typen och omvandlar det punk- tabsorberande systemet rörelse till el. För att testa denna generator- modell så påbörjades bygget av två fullskaliga prototyper 2017. Denna uppsats behandlar specifikt arbetet med generatorlindningen till pro- totyperna och innefattar processen från design till själva byggnatio- nen. Lindingen består av flertalet mindre och isolerade lindningsleda- re med uppgift att bland annat minska skinneffekt och virvelströms- förluster. När man använder denna metod så uppkommer dock ett nytt problem vilket härstammar från att lindningsledarna är samman- kopplade i vardera ända och bildar på så sätt n slutna strömkretsar. Konsekvensen kan vara stora förluster från cirkulerande strömmar på grund av det magnetiska ströflöde som finns runt järnkärnan som lindningen omsluter. Utgångspunkten för att minimera dessa cirkule- rande strömmar är att transponera alla lindningsledare på ett sätt så att den resulterande elektromotoriska spänningen för varje strömkrets blir så liten som möjligt. Med hjälp av förenklade modeller samt FEM simuleringar så bestämdes ett lämpligt sätt att transponera lindningstrådarna utifrån oli- ka kriterier. Lösningen blev att lindningstrådarna endast transponera- des en gång med en så kallad 180 grader transponering. Detta ger en tillräckligt god minimering av de cirkulerande ström- marna, men den stora fördelen med denna lösning är att det är möjligt att linda maskinen med de små resurser projektet hade tillgång till, dock var detta till en stor nackdel då väldigt mycket tid gick till att hitta egna tillvägagångsätt för att utföra byggandet av lindningen på ibland okonventionella sätt.